1. Field of the Invention
This invention relates to the characterization and processing of optical beams, and more particularly to a system and method for detecting and adaptively thresholding a two dimensional image or data pattern via a quasi-one-dimensional planar, positionally mapped intensity spectrum of a light beam for re-transformation to a two-dimensional thresholded output.
2. Description of the Related Art
Optical computing and logic processing may be performed by using the optical intensities distributed across a light beam. This may be accomplished by first converting the distribution of optical intensities to a positional mapping, and then operating upon the signal at each different position to perform the desired computing or processing. The meaning of "light" or "optical" as used throughout this specification is not limited to wavelengths of the visible range, but should be understood to encompass the entire electromagnetic spectrum of wavelengths including, for example, infrared.
A system which accomplishes the desired intensity-to-position mapping is described in U.S. Pat. No. 4,351,589 to pierre H. Chavel et al., assigned to Hughes Aircraft Company, the assignee of the present invention. The patent discloses the use of liquid crystals to produce variable gratings, which diffract incoming light by varying amounts depending upon the grating period. The optical intensities at the different locations in an input light beam control the grating period at corresponding locations in the liquid crystal media. The variable gratings convert the spatial intensity distribution of the input beam to a positional mapping of intensities, from which the desired computing and logic functions can be accomplished.
Other systems to accomplish the intensity-to-position mapping are disclosed in U.S. patent application Ser. No. 879,719, "Optical Intensity-To-Position Mapping Apparatus and Method" by Bernard Soffer and U.S. patent application Ser. No. 900,053, "Light Deflector Apparatus and Method" by Yuri Owechko, both applications being assigned to Hughes Aircraft Company, the assignee of the present invention. Messrs. Soffer and Owechko are also the inventors of the present invention. Their prior systems disclose methods of using diffraction principles different from the variable grating-based system disclosed in the Chavel et al. patent. By varying the refractive indices of an array of small, variable refraction modules provided to receive an input light beam with optical intensities that vary as a function of position with the beam, the input optical intensities are mapped onto an array of optical output directions from the modules.
With any of the above-referenced systems, the mapping process yields a number of discrete spots, the intensity of each spot corresponds to the number of pixels in the input light beam which have an optical intensity corresponding to the position of said spot. This representation is called a histogram.
Once a histogram has been obtained, it may be used as a thresholding mechanism for blocking portions of the original beam which fail to exceed a given threshold, such as a predetermined multiple of standard deviations or variances of the original optical beam intensity distribution. The predetermined multiple can also be time-varying, and is selected to provide the intensity threshold desired. Histogram processing on serial electronic computers is relatively slow because all of the pixels in the input image must be processed for each histogram bin.
Another optical processing method created by Hughes Aircraft Company, the assignee of the present invention, utilizes a phase-conjugate resonator configuration. The phase conjugate resonator provides for the non-mixing of transverse modes, thereby allowing spatially disparate regions to reach the threshold of oscillation independently. This method uses a fixed, rather than variable, threshold and is still subject to noise.